The present invention relates to the use and application in LED array display, optical communication and mobile computing. A review of these technologies are provided below as the background of the present invention.
LED array display board is a popular instrument for commercial usage. Many banks, shops and cinemas are willing to install one piece of it because of its versatility. LED array display board can be very bright and eye-catching. Thus, it is very suitable for advertising purpose. Also, unlike printed sign or logo, the message displayed on the LED array can be changed all the time. One can use it to tell people what is the most updated information in real-time. For example, in a bank, it is used to show the current stock market value, currency exchange rate and interests rate. In a shop, it can be used to tell people what is the opening hour, what is the biggest bargain today, etc.
The features and functionality of LED array display board also becomes more enriched. Scrolling, blinking, built-in character formats are just some basic functions. More powerful LED array can have a multi-color display. The resolution is enhanced by reducing the dot size and have LEDs packed more closely. The size of the array also becomes larger and larger. The smallest LED array starts with a single line text display. But some huge LED array can be taller than a man, have multi-line text and even graphics display. Nevertheless, existing LED display board is only used to give visual message (or image) display. It can do nothing more than this.
Free space optical communication (FSOC) is often used for short-range communication purpose. It is quite extensively used and popular, since the usage of optical frequency is not regulated by telecommunication authority. Some typical examples are TV remote control, toll collection, etc. A FSOC system mainly consists of a LED for transmitting light wave and a photodetector for converting an optical signal into an electrical signal. One may have other front-end circuit elements, such as optical filter, low noise amplifier, data and clock recovery circuit, etc.
An important point to note is that possible wavelengths used in optical communication ranges from the visible light region to the infrared region. However, most present FSOC systems use the infrared region. They are often referred to as infrared communication system. This may be due to the fact that those semiconductor devices (LED and photodetector) are more optimized in the infrared region. Nevertheless, visible light can also be a candidate for optical communication. Indeed, most LEDs do not emit light wave of a single wavelength.
The confluence of portable computers and wireless communication has led to the emergence of mobile computing. Mobile computing usually requires certain form of wireless network so that the mobile computer can get connected at pre-defined locations. Existing wireless network packages often utilize the atmospheric spectrum of ISM band or UHF band. Some uses the infrared spectrum.
Mobile computing is an attractive technology to most people who need to travel around and do not stay in a fixed office space. The potential user pool is very great. But some problems that hinder the growth of mobile computing include low communication bandwidth and high system cost. Existing wired network facilities also are not quite optimized for the purpose of mobile computing.